Fiber optic receivers typically deal with very low signal levels. For example, a typical receiver preamp input signal level is on the order of 2-10 .mu.A, while a typical receiver postamp input signal level is on the order of 10-15 mV. These low voltage levels are generally amplified prior to their processing by digital circuitry, which usually requires signal levels of at least 0.4-1 V.
GaAs circuitry can operate over a very large frequency range, from DC to a few gigahertz. However, designing D.C. coupling in GaAs is difficult because of the great variability of operational characteristics with process and temperature. For example, the V.sub.GS of a GaAs transistor may vary as much as 400 mV over process and temperature for a given current. Thus, GaAs appears to be an impractical process for precisely level-shifting and amplifying signals from fiber optic transceivers using low voltage power supplies.